Method of cleaning metal articles



V Patented June 14, 1938 UNITED STATES PATENT OFFICE Floyd M. Hanger,Chicago, Ill.,. assignor to Keystone Steel & Wire Company, Peoria, 111.,a

corporation of Illinois Application September 25, 1935,

Serial No. 42,029

No Drawing.

1 Claim.

This invention has reference to a method of cleaning metallic articleswhich are to be coated with a protective coating of zinc.

The invention is especially adapted to iron or steel articles such aswire, although it may be found readily adaptable to other ferrousarticles, as for example iron or steel sheets, strips and similararticles.

The invention has for its principal object to improve the zinc coatingof iron or steelarticles, as for example wire, sheets, strips and thelike, made from rimmed or open steel.

The invention has for a further object, the cleaning and preparing thesurface of the metallic articles, before galvanizing, by subjecting thearticle to a molten bath of a mixture of sodium carbonate and potassiumcarbonate, which is a preferred method; or the article may be subjectedto a water paste, made up of either sodium carbonate or potassiumcarbonate or a mixture of the two, and subsequently anneal the articleto the preferred physical properties, and then coat the article with aprotective coating of zinc. Employing a molten bath of salts consistingof a mixture of sodium carbonate and potassium carbonate I am enabled toanneal the article and at the same time the bath will act upon thesurface of the article so as to clean and etch such surfaces and preparesaid surface to take a more adherent heavy coating of zinc. In the useof the saturated water solution the article is first treated with thesolution and then subsequently annealed and galvanized.

In practicing the invention, I prefer to treat the article so as toclean and prepare its surface for the applicatipn of the zinc coating,by subjecting the same to the combined salts, sodium carbonate andpotassium carbonate, in a molten state. Such a bath is convenient andexpedient and by its use it is possible to anneal the metallic articleto the desired physical strength and obtain the cleaning and preparationof the surface of the article, at the same time. The same beneficialresults, however, may be obtained by subjecting the article to a waterpaste made up of eithersodium carbonate or potassium carbonate or amixture of the two, and subsequently anneal the article to the preferredphysical properties.

Of the water solutions, which may be used, I pre- I have discovered inthe use of the molten bath of a mixture of the sodium carbonate andpotassium carbonate that the bath has no carburizing effect on thearticle and as far as I have been able to find, has no effect exceptthat it is slightly oxidizing. Experience in the use of the inventionleads me to believe that the sodium oxide which is formed by thedecomposition of the salt has a tendency to etch the iron or steelaround the grain boundaries and I have found that the bath of theinvention gives a cleaner surface on the article thanis obtained by anyordinary treatment.

The temperature of the molten bath may range from l250 to 1400 F. I haveobtained the most satisfactory results employing a temperature between1325 and 1350 F.

Sodium carbonate or potassium carbonate may be used alone in the moltencondition and correspondingly similar results obtained, but temperaturesranging from l550 to 1750 F. must be used. However, if such hightemperatures are used, a very soft wire is produced. The temperaturerange at which the molten salt could be operated would, of course,depend on the physical properties desired in the article. In thetreatingand coating of iron or steel wire, I have obtained the besttensile strength and other physical properties when the combination withsalts is used at the specified temperature of 1325" to 1350 F.

I wish to point out, that there is no carburizing or nitriding effectobtained by the use of sodium carbonate or potassium carbonate alone, orin combination. When these salts are heated they decompose as isillustrated by the following formula: NazCOs give NazO-COz. As can beseen this decomposition will give an oxidizing bath which is exactly theopposite of carburizing.

I am aware that efforts have been made to anneal iron or steel articlesin certain molten would be first subjected to such a bath which wouldboth treat the surface of the article and anneal the same. Assuming thearticle to be an iron or steel wire, it would pass from the bath throughan acid tank and be finally coated with a. protective coating of zinc.By the method described for cleaning and preparing the surface of thearticle, the surface is made-more susceptible to the attack by the zincand thus alloys better, giving a firmer bond. In the second instance,that is employing a saturated solution of 15 ture of sodium carbonateand potassium carbonate ,or each of these compounds used alone. Further-.more, iron or steel articles may be successfully treated and galvanizedby the use of the water solution of a mixture of these salts, or eachalone,

and the article subsequently annealed, to obtain the necessary physicalproperties.

It is obvious that those skilled in the art may vary the details of theprocedure without departing from the spirit of the invention, andtherefore it is not desired to be limited to the above disclosure exceptas may be required by the claim.

What I claim is: v

The process of treating the surface of a body of rimmed or open steelprior to'the application of a zinc coating thereon, which consists inchemically roughenlng the surface of the body by immersing the same in amolten bath of an alkaline carbonate for a sufllcient time to effect an.

opening of the exposed grain boundaries, and then subjecting the treatedbody to a pickling operation to cleanse the roughened surface.

FLOYD M. HAUGER.

